The present invention relates to a method for controlling pressure in a compressed-air accumulator of a level-control system of a motor vehicle.
Methods of the general type under consideration are known, for example, from DE 101 22 567 C1 and DE 101 60 972 C1.
A level-control system for a vehicle is typically provided at each wheel suspension of the vehicle with an air spring bellows to which compressed air can be supplied or from which compressed air can be removed via a valve device. Usually, a compressor is provided to generate the compressed air. To achieve short times for filling and venting the air spring bellows and thus short times for raising and lowering the vehicle body, and to save on the energy required for this purpose, it is advantageous to design such a level-control system as a closed or partly closed system containing a compressed-air accumulator. The compressor is then used primarily to transport compressed air back and forth between the compressed-air accumulator and the air spring bellows. Depending on the operating condition of the vehicle and on external ambient conditions, a variable pressure level in the compressed-air accumulator may be advantageous for achieving short times for filling and venting the air spring bellows and for achieving low energy consumption.
DE 101 60 972 C1 describes how to control the air quantity in a level-control system, while also taking the ambient temperature of the vehicle into consideration via a temperature sensor. For this purpose, a separate temperature sensor for measuring the ambient temperature is necessary.
DE 101 22 567 C1 describes controlling the pressure in the compressed-air accumulator indirectly by determining the air quantity in the level-control system. For simplicity, in determining the air quantity in the level-control system, it is assumed that this quantity is composed of individual air quantities in the air spring bellows and in the compressed-air accumulator and that the individual air quantities in the air spring bellows can be calculated from measured values of pressure and height sensors.
Conventionally, the physical variables relevant for control of the accumulator pressure are taken into consideration not at all or only inadequately. For example, the ambient temperature is not an essential physical variable that determines the efficiency of operation of the level-control system. Even determination of the air quantity does not lead to a physical variable by means of which satisfactory efficiency can be achieved during operation of the level-control system.
Accordingly, the object of the invention is to provide, for control of the pressure in a compressed-air accumulator of a level-control system for a motor vehicle, a method that permits efficient operation of the level-control system. It should be understood that efficient operation of the level-control system is characterized by, for example, low energy consumption, short times for raising and lowering the vehicle body, and the capability of using a compressor designed for the smallest possible delivery capacity.